(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of improving the adhesion of molding compound over the surface of a passivation layer by first creating an oxygen rich layer over the surface of the layer of passivation.
(2) Description of the Prior Art
The creation of semiconductor devices entails the creation of interactive circuit elements in or on the surface of a substrate. After these circuit elements have been created, the semiconductor die is further processed which in many cases implies,the further mounting of a singulated die into a semiconductor package. Before the final processing of the semiconductor device takes place, the device needs to be protected against damage that can be inflicted on the devices by chemical reaction with surrounding elements or by mechanical damage such as scratching of the surface of the device. For these reasons a layer of passivation material is typically deposited over the surface of the completed device. The passivation layer that is deposited over the surface of the device coats the device with a protective layer. For layers of passivation to meet the objective of protecting the surface of the underlying device, such layers must be resistant to thermal and mechanical stress and must further form a barrier against chemical reaction of the surface of the device with surrounding elements.
After a semiconductor device has been created, measures must be taken to interconnect the device to surrounding circuitry. For this purpose, bond pads are created on the surface of the device by depositing a layer of metal, typically aluminum, over the surface of the device. The layer of metal is patterned and etched creating bond pads that can be interconnected with contact points provided on the surface of the semiconductor device. After the bond pads have been created, the surface of the device is typically covered with a layer of passivation wherein openings are provided for the establishment of electrical contacts with the created bond pads. The thus completed device is next packaged, the main objectives of the device packaging are to protect the device against external influences (dust, heat, moisture, chemicals, electrically charged particles) and mechanical influences (scratching, breakage of the device, heat stress). The device package further serves as the main electrical interconnect interface between the device and surrounding electrical components.
The essential advantages that are gained by packaging the semiconductor device have already been highlighted. One of the disadvantages that is incurred as a result of the packaging of the device is due to the fact that aluminum is prone to corrode when exposed to moisture. Moisture penetrates the plastic material that is typically used for the device package and will cause corrosion in sensitive interfaces of the device and the package such as variations in density of the plastic material (cracks) or in any opening that may exist between the mounted die and the lead frame on which the die is mounted. Frequently attacked by corrosion are also points of interconnect of the die, such as the contact point where a bond wire is connected to a bond pad.
It is clear that in packaging semiconductor devices all interfaces that are established within the package must be solid and firm interfaces without the occurrence of any openings or surface irregularities that lend themselves to the accumulation of impurities and moisture with subsequent results of corrosion, high resistivity contact points, problems of reliability and the like. In addition, the interface between the layer of passivation and the overlying plastic material that encases the device must be mechanically strong so that the bond that is formed between the layer of passivation and the overlying plastic material (epoxy) is stress resistant. The invention provides a method that increases the adhesion strength between the surface of the layer of passivation that has been deposited over the die and the molding compound. The invention further eliminates problems of surface delamination of the interface between the die surface and the overlying molding compound.
U.S. Pat. No. 5,595,934 (Kim) shows forming an oxide protective film on a bond pad.
U.S. Pat. No. 6,096,649 (Jang) reveals a method to roughen the surface to improve adhesion.
U.S. Pat. No. 6,046,071 (Sawai et al. al.) and U.S. Pat. No. 5,883,001 (Jin et al.) are related patents.
A principle objective of the invention is to increase the adhesion strength between a layer of passivation that has been deposited over the surface of a semiconductor die and an overlying molding compound.
Another objective of the invention is to provide a post nitride oxide of oxide treatment to the surface of a layer of passivation in order to increase adhesion strength between the layer of passivation and an overlying layer of epoxy.
Yet another objective of the invention is to eliminate delamination in the interface between a layer of passivation and an overlying layer of epoxy.
In accordance with the objectives of the invention a new method is provided for treating the surface of a layer of passivation where this layer of passivation comprises silicon dioxide or silicon nitride. An oxygen rich layer is created over the surface of the layer of passivation.
Under the first embodiment of the invention a layer of silicon oxide is deposited over the surface of a substrate, a layer of plasma enhanced silicon nitride is deposited over the surface of the layer of silicon oxide, and a layer of oxynitride is deposited over the surface of the layer of plasma enhanced silicon nitride,
Under the second embodiment of the invention a layer of silicon oxide is deposited over the surface of a substrate, a layer of silicon nitride is deposited over the surface of layer of silicon oxide. The surface of the layer of silicon nitride is oxidized.